Differential hemodynamic adaptations to tilt test in patients with idiopathic atrial fibrillation

The hemodynamic response during the transition from the supine to standing position in idiopathic atrial fibrillation (AF) patients is not completely understood. This study aimed to analyze the hemodynamic changes that occur during the head-up tilt test in idiopathic AF patients. We investigated the hemodynamic changes during the head-up tilt test with impedance cardiography in 40 AF patients (12 with AF rhythm-AFr and 28 with sinus rhythm-AFsr) and 38 non-AF controls. Patients with AFr had attenuated SVI decrease after standing when compared to AFsr and non-AF [ΔSVI in mL/m2: -1.3 (-3.4 to 1.7) vs. -6.4 (-17.3 to -0.1) vs. -11.8 (-18.7 to -8.0), respectively; p < 0.001]. PVRI decreased in AFr but increased in AFsr and non-AF [ΔPVRI in dyne.seg.m2/cm5: -477 (-1148 to 82.5) vs. 131 (-525 to 887) vs. 357 (-29 to 681), respectively; p < 0.01]. Similarly, compared with non-AF patients, AFr patients also had a greater HR and greater CI increase after standing. The haemodynamic response to orthostatic challenge suggests differential adaptations between patients with AF rhythm and those reverted to sinus rhythm or healthy controls. Characterizing the hemodynamic phenotype may be relevant for the individualized treatment of AF patients.

Longitudinal study on the effect of surgical weight loss on beat-to-beat blood pressure variability in patients undergoing bariatric surgery: a study protocol

INTRODUCTION

Alterations in linear and non-linear parameters of beat-to-beat blood pressure variability (BPV) have been shown to predict disease prognosis and distinguish between risk categories in various pathological conditions, independently of average blood pressure levels. Obesity places subjects at elevated risk of vascular diseases, including hypertension, resulting in serious cardiac, respiratory and cerebral events. However, little is known about the status of vascular dynamics in obese and morbidly obese adults.

METHODS AND ANALYSIS

In this present quasi-experimental longitudinal study, changes in beat-to-beat BPV, using continuous, non-invasive blood pressure monitoring, in obese subjects undergoing bariatric surgery are characterised. The capacity of linear and non-linear measures of BPV to detect differences between hypertensive, prehypertensive and normotensive obese subjects prebariatric and postbariatric surgery are tested. Additionally, potential correlations between beat-to-beat BPV and age, body mass index, gender and comorbidities will be investigated. In parallel, the impact of the unsteady fluctuations of beat-to-beat blood pressure on the dynamic stresses imparted by blood flow on blood vessel walls will be explored. We expect to find altered BPV profiles in hypertensive and prehypertensive subjects as compared with normotensive subjects. We also expect to see differential normalisation in BPV profiles between hypertensive, prehypertensive and normotensive subjects over time.

ETHICS AND DISSEMINATION

The study has been approved by the Institutional Review Board at the American University of Beirut (IRB ID: BIO-2018-0040). Study results will be made available to the public through publications in peer-reviewed journals and conference papers and/or presentations.

Beat-to-beat blood pressure variability: an early predictor of disease and cardiovascular risk

Blood pressure (BP) varies on the long, short and very-short term. Owing to the hidden physiological and pathological information present in BP time-series, increasing interest has been given to the study of continuous, beat-to-beat BP variability (BPV) using invasive and noninvasive methods. Different linear and nonlinear parameters of variability are employed in the characterization of BP signals in health and disease. Although linear parameters of beat-to-beat BPV are mainly measures of dispersion, such as standard deviation (SD), nonlinear parameters of BPV quantify the degree of complexity/irregularity- using measures of entropy or self-similarity/correlation. In this review, we summarize the value of linear and nonlinear parameters in reflecting different information about the pathophysiology of changes in beat-to-beat BPV independent of or superior to mean BP. We then provide a comparison of the relative power of linear and nonlinear parameters of beat-to-beat BPV in detecting early and subtle differences in various states. The practical advantage and utility of beat-to-beat BPV monitoring support its incorporation into routine clinical practices.

Low Computational Cost for Sample Entropy

Sample Entropy is the most popular definition of entropy and is widely used as a measure of the regularity/complexity of a time series. On the other hand, it is a computationally expensive method which may require a large amount of time when used in long series or with a large number of signals. The computationally intensive part is the similarity check between points in m dimensional space. In this paper, we propose new algorithms or extend already proposed ones, aiming to compute Sample Entropy quickly. All algorithms return exactly the same value for Sample Entropy, and no approximation techniques are used. We compare and evaluate them using cardiac inter-beat (RR) time series. We investigate three algorithms. The first one is an extension of the kd-trees algorithm, customized for Sample Entropy. The second one is an extension of an algorithm initially proposed for Approximate Entropy, again customized for Sample Entropy, but also improved to present even faster results. The last one is a completely new algorithm, presenting the fastest execution times for specific values of m, r, time series length, and signal characteristics. These algorithms are compared with the straightforward implementation, directly resulting from the definition of Sample Entropy, in order to give a clear image of the speedups achieved. All algorithms assume the classical approach to the metric, in which the maximum norm is used. The key idea of the two last suggested algorithms is to avoid unnecessary comparisons by detecting them early. We use the term unnecessary to refer to those comparisons for which we know a priori that they will fail at the similarity check. The number of avoided comparisons is proved to be very large, resulting in an analogous large reduction of execution time, making them the fastest algorithms available today for the computation of Sample Entropy.

Effect of salt intake on beat-to-beat blood pressure nonlinear dynamics and entropy in salt-sensitive versus salt-protected rats

Blood pressure exhibits substantial short- and long-term variability (BPV). We assessed the hypothesis that the complexity of beat-to-beat BPV will be differentially altered in salt-sensitive hypertensive Dahl rats (SS) versus rats protected from salt-induced hypertension (SSBN13) maintained on high-salt versus low-salt diet. Beat-to-beat systolic and diastolic BP series from nine SS and six SSBN13 rats (http://www.physionet.org) were analyzed following 9 weeks on low salt and repeated after 2 weeks on high salt. BP complexity was quantified by detrended fluctuation analysis (DFA), short- and long-range scaling exponents (αS and αL), sample entropy (SampEn), and traditional standard deviation (SD) and coefficient of variation (CV(%)). Mean systolic and diastolic BP increased on high-salt diet (P < 0.01) particularly for SS rats. SD and CV(%) were similar across groups irrespective of diet. Salt-sensitive and -protected rats exhibited similar complexity indices on low-salt diet. On high salt, (1) SS rats showed increased scaling exponents or smoother, systolic (P = 0.007 [αL]) and diastolic (P = 0.008 [αL]) BP series; (2) salt-protected rats showed lower SampEn (less complex) systolic and diastolic BP (P = 0.046); and (3) compared to protected SSBN13 rats, SS showed higher αL for systolic (P = 0.01) and diastolic (P = 0.005) BP Hypertensive SS rats are more susceptible to high salt with a greater rise in mean BP and reduced complexity. Comparable mean pressures in sensitive and protective rats when on low-salt diet coupled with similar BPV dynamics suggest a protective role of low-salt intake in hypertensive rats. This effect likely reflects better coupling of biologic oscillators.

Atrial fibrillation, CHA2DS2-VASc score, antithrombotics and risk of non-traffic-, non-cancer-related bone fractures: A population-based cohort study

BACKGROUND

Accidental bone fractures are a major cause of premature disabilities and death. Whether atrial fibrillation (AF) treated with or without antithrombotics correlates with occurrence of such events remains under-investigated.

METHODS

Patients ≥18 years with newly diagnosed AF between 2005 and 2009 without previous cancers or traffic injury were identified from the "Longitudinal Health Insurance Database 2005" (1 million beneficiaries) of Taiwan's National Health Research Institutes and served as the AF group. A fourfold number of age-, gender-, and comorbidity-matched patients but without AF served as the non-AF controls. Patients were followed, and cumulative incidence of hospitalization-requiring bone fractures was compared between groups. Predictors of accidental bone fractures were determined by Cox regression analysis.

RESULTS

Within a mean follow-up of 3.6 years, bone fractures, especially those involving neck/trunk and lower limbs, were significantly more frequent in patients with AF (N=6925) than in those without (N=27,700) (7.0 vs. 3.8 per 1000 person-years, log-rank p=0.001, adjusted HR=1.85, 95% CI=1.50-2.30, p<0.001). Cox models identified female gender, previous stroke, and CHA2DS2-VASc score≧1 as risk factors for bone fractures in AF patients, whereas oral anticoagulants (HR=0.62, 95% CI=0.35-0.91, p=0.034), especially when used in patients with CHA2DS2-VASc score≧1 but not antiplatelet therapy (p=0.39) as negative predictors.

CONCLUSION

Patients with AF are more vulnerable to non-traffic-, non-cancer-related bone fractures especially when with specified characteristics. For those with higher CHA2DS2-VASc scores, the use of anticoagulant but not antiplatelet agents could be associated with lower risk of such events.

Atrial fibrillation, CHA2DS2-VASc score, antithrombotics and risk of traffic accidents: A population-based cohort study

BACKGROUND

Traffic accidents account for a substantial proportion of premature disabilities and deaths. Whether atrial fibrillation (AF) provokes while antithrombotics prevent from such events remains un-investigated.

METHODS

All patients ≥40years with newly diagnosed AF in 2005 were scrutinized from the "Longitudinal Health Insurance Database 2005" (1 million beneficiaries) of Taiwan's National Health Insurance Institute as the AF group. Four-fold number of age-, gender-, and comorbidity-matched patients but without AF served as the Non-AF controls. Patients were followed till occurrence of hospitalization-requiring traffic injury, death, withdrawal from insurance, or the end of 2010. Cumulative incidence of traffic accidents was compared between groups, and predictors and preventive role of antithrombotics for these accidents were identified by Cox regression analysis.

RESULTS

Within a mean follow-up of 4.3years, traffic injury occurred significantly more often in patients with AF (N=1724) than those without it (N=6896) (5.4 vs. 4.9 per 1000 person-years, log-rank p=0.012, HR 1.110, 95% CI 1.013-1.572). Cox models identified age ≧65years, hypertension, coronary artery disease, stroke, liver cirrhosis and CHADS2VASC score≧1 as risk factors for traffic injury in AF patients, whereas oral anticoagulants (HR 0.576, 95% CI 0.285-0.791, p=0.002) used in patients with CHADS2VASC score ≧1 but not antiplatelet therapy (p=0.197) as negative predictors.

CONCLUSION

Patients with AF are more vulnerable to traffic accidents especially when with higher CHADS2VASC scores and other comorbidities. This tendency to traffic accidents, however, could be ameliorated by oral anticoagulation in specialized cases but not by antiplatelet therapy.